Nitrogen dioxide is a ubiquitous air pollutant resulting from the combustion of fossil fuels. Indoor levels of nitrogen dioxide are often higher than outdoor concentrations, especially in homes where there are unvented heating and cooking appliances that utilize natural gas, kerosene, coal, or wood. Drs. John Spengler, Jonathan Samet, and their colleagues determined the impact of housing characteristics and the type and use of cooking ranges on nitrogen dioxide levels in infants' bedrooms in Albuquerque.